Lipochitooligosaccharides are naturally made in rhizobial bacteria and function as nodulation factors. The nodulation factors secreted from the bacteria elicit a response in the root cells of legumes that leads to symbiotic nodule formation in the roots. In these nodules nitrogen is fixed, and is provided as a nutrient to the plant. The extent of legume root nodulation is directly linked to plant growth and productivity.
The nodulation factor lipochitooligosaccharides have a backbone of four or five β1,4-linked N-acylated glucosamine residues, a structure also found in chitin (poly-[1-4]-β-N-acetyl-D-glucosamine). This backbone is N-acylated and can carry diverse substitutions at both ends, depending on the rhizobial species in which it is made. In some rhizobia the N-acylation of the terminal unit is with fatty acids of general lipid metabolism such as vaccenic acid (C18:1Δ11Z) and in other rhizobia the N-acylation is with polyunsaturated fatty acids such as C20:3 and C18:2.
The nodulation factor lipochitooligosaccharides made in any one species of bacteria are a mixture of compounds having different substitutions that are not possible to completely separate. Some nodulation factor lipochitooligosaccharides have been chemically synthesized. There are various reported methods for making small samples of lipochitooligosaccharides, for example as described in Nicolaou et al., J. Am. Chem. Soc. 114: 8701-8702 (1992); Ikeshita et al., Carbohydrate Research C1-C6 (1995); and Wang et al., J. Chem. Soc. Perkin Trans. 1: 621-628 (1994).
There remains a need for a process to make the lipochitooligosaccharide class of N-acylglucosamine oligomers in larger quantities and economically. The present invention is related to these and other ends.